1. Field of the Invention
The present invention relates generally to medical ultrasound systems and, more particularly, to a diagnostic and/or therapeutic catheter providing a plurality of ultrasound transducers within a distal end of a drive shaft.
2. Background of the Invention
Intraluminal, intracavity, intravascular, and intracardiac diagnosis and treatment of medical conditions utilizing minimally invasive procedures is an effective tool in many areas of medical practice. These procedures typically are performed using imaging and treatment catheters that may be inserted into either an opening in a patient""s body or percutaneously into an accessible vessel, such as the femoral artery, of the vascular system at a site remote from a region of the patient""s body to be diagnosed and/or treated. The catheter then may be advanced, for example, through the vessels of the vascular system to the region of the patient""s body to be diagnosed and/or treated, such as a vessel or an organ. The catheter may be equipped with an imaging device, typically an ultrasound imaging device, which may be used to locate and diagnose a diseased portion of the patient""s body, such as a stenosed region of an artery. The catheter may alternatively include an ultrasound transducer for therapeutically treating or, if desired, disintegrating the diseased portion of the patient""s body.
Intravascular imaging systems having ultrasound imaging capabilities generally are known. For example, U.S. Pat. No. 4,951,677, issued to Crowley, the disclosure of which is incorporated herein by reference, describes an intravascular ultrasound imaging system. An ultrasound imaging system typically contains some type of control system, a drive shaft, and a transducer assembly including an ultrasound transducer. The transducer assembly includes a transducer element and is coupled to the control system by the drive shaft. The drive shaft typically permits communication between the control system and the ultrasound transducer.
In operation, the drive shaft and the transducer assembly are inserted, usually within a catheter, into a patient""s body and may be positioned near a remote region. To provide diagnostic scans of the remote region within, for example, a coronary blood vessel, the ultrasound transducer may be positioned near or within the remote region of the patient""s body. Diagnostic scans are created when the control system alternately excites and allows sensing by the ultrasound transducer. The control system may direct the ultrasound transducer toward an area of interest within the remote region. When the ultrasound transducer is excited, the ultrasound transducer creates ultrasound waves in the bodily fluids surrounding the ultrasound transducer. The ultrasound waves then propagate through the fluids within the patent""s body and ultimately reach the area of interest, forming reflected ultrasound waves. The reflected ultrasound waves then return through the fluids within the patient""s body to the ultrasound transducer, inducing electrical signals within the ultrasound transducer. The control system then may collect the induced electrical signals and may reposition the ultrasound transducer to an adjacent area within the remote region of the patient""s body, again exciting and sensing the ultrasound transducer. This process may continue until the remote region has been examined sufficiently and a series of induced signals has been collected. The control system then may process the series of induced signals to derive a diagnostic scan and may display a complete image of the diagnostic scan.
Ultrasound waves may also be used to therapeutically treat or, if desired, disintegrate a diseased portion of a patient""s body. Intraluminal systems and catheters for providing ultrasound therapy are generally known. For example, U.S. Pat. No. 5,471,988, issue to Fujio et al., the disclosure of which is incorporated herein by reference, describes such an intraluminal ultrasound therapy system. Like the ultrasound imaging system, an ultrasound therapy system generally includes a control system and a transducer assembly, each communicating with a drive shaft. However, whereas ultrasound imaging systems typically use low intensity ultrasound waves, ultrasound therapy systems may require higher intensity ultrasound waves than the ultrasound waves used for imaging or diagnosis.
As in the ultrasound imaging system, the drive shaft and the transducer assembly of the ultrasound therapy system are inserted, usually within a catheter, into a patient""s body and may be positioned near a remote region to be treated. When the control system excites the transducer assembly directed toward the area of interest, high intensity ultrasound waves may propagate from the ultrasound transducer and toward the area of interest. When the ultrasound waves reach the area of interest, the ultrasound waves may cause the area of interest to begin to vibrate. This vibration may cause the area of interest to be therapeutically heated to relieve pain or become stimulated or relaxed. If the area of interest is undesired, ultrasound waves may be transmitted at a resonant or critical frequency of the area of interest; thereby, the area of interest may be disintegrated. The control system may continue to excite the ultrasound transducer until the therapy has been completed.
Medical ultrasound systems for diagnosis and treatment, however, currently suffer from several deficiencies. First, the available resolution of the resultant diagnostic scans could be increased. Typical medical ultrasound systems utilize only a fundamental harmonic of the ultrasound waves generated by the ultrasound transducer. Additional resolution may be possible by also examining higher order harmonics of the ultrasound waves. Second, the size of the area of interest that may be treated by current medical ultrasound systems remains relatively small. Therapeutic catheters treat regions of a patient""s body by directing intense ultrasound waves toward an area of interest in a patient""s body. The intense ultrasound waves may induce the area of interest to vibrate, causing the area of interest to grow warm. A single transducer, however, may be focused only on a small region; thus, requiring individual regions of a large area of interest to be treated separately. Patients may benefit from having the entire area of interest treated simultaneously. Third, the ultrasound waves may suffer from attenuation during propagation through a patient""s body. When the ultrasound transducers explore deeper into the patient""s body, the ultrasound transducers may need to be reduced physically in size to fit within smaller regions, but, as the size of the ultrasound transducer decreases, the center frequency of the ultrasound transducer may increase. Since higher frequency ultrasound waves may be more subject to attenuation than lower frequency ultrasound waves, the depth of penetration of the higher frequency ultrasound waves may be limited.
In view of the foregoing, it is believed that a need exists for an improved catheter that overcomes the aforementioned obstacles and deficiencies of currently available diagnostic and therapeutic catheters.
The present invention is directed to a diagnostic and/or therapeutic catheter incorporating a drive shaft with a distal end having a plurality of ultrasound transducers for providing therapeutic treatment to or creating diagnostic images of an area of interest within a patient""s body. The present invention provides the advantages of improved image resolution, enhanced ability to excite the area of interest, and increased penetration depth for diagnosis.
In one preferred form, a catheter in accordance with the present invention may comprise a drive shaft, a first ultrasound transducer for transmitting ultrasound waves, and a second ultrasound transducer and a third ultrasound transducer each for receiving ultrasound waves. The drive shaft may have a proximal end, rotatably communicating with an ultrasound imaging system, and a distal end. The first ultrasound transducer preferably is mounted on the distal end of the drive shaft and may have a preselected center frequency. The second ultrasound transducer may be mounted on the distal end of the drive shaft at a preselected distance from the first ultrasound transducer and may have a preselected center frequency substantially equal to a fundamental harmonic of ultrasound waves generated by the first ultrasound transducer. The third ultrasound transducer preferably is mounted on the distal end of the drive shaft at a preselected distance from the first ultrasound transducer and may have a preselected center frequency substantially equal to a second harmonic of the ultrasound waves generated by the first ultrasound transducer. The second ultrasound transducer and the third ultrasound transducer each preferably are directed to receive the fundamental harmonic and the second harmonic, respectively, of reflections of the ultrasound waves generated by the first ultrasound transducer.
In a second preferred embodiment, the second ultrasound transducer preferably transmits ultrasound waves and may have a center frequency substantially equal to the center frequency of the first ultrasound transducer. The first ultrasound transducer and the second ultrasound transducer each may be directed at a first end and a second end, respectively, of an area of interest, such as a tissue segment. When the first ultrasound transducer and the second ultrasound transducer are excited, the area of interest may be therapeutically treated or, if the area of interest is undesired, disintegrated.
In a third preferred embodiment, the second ultrasound transducer may be capable of transmitting and receiving ultrasound waves and preferably has a center frequency that differs from the center frequency of the first ultrasound transducer. The third ultrasound transducer preferably has a center frequency that is substantially equal to a difference between the fundamental harmonic of the ultrasound waves generated by the first ultrasound transducer and a fundamental harmonic of the ultrasound waves produced by the second ultrasound transducer. The first ultrasound transducer and the second ultrasound transducer may be directed such that the ultrasound waves of the first ultrasound transducer preferably converge with the ultrasound waves of the second ultrasound transducer, creating difference ultrasound waves. The ultrasound waves created by the second ultrasound transducer and the difference ultrasound waves each may be reflected by an area of interest and, thereafter, received by the second ultrasound transducer and the third ultrasound transducer, respectively.
It will be appreciated that a catheter having a plurality of ultrasound transducers in accordance with the present invention may increase the utility of diagnostic and/or therapeutic catheters. By analyzing both the fundamental harmonic and the second harmonic of the ultrasound waves of the first ultrasound transducer, more information about an area of interest may be available to the medical ultrasound system, and diagnostic images with higher resolutions may result. For example, soft tissues may reflect certain harmonics of the ultrasound waves better than other harmonics of the ultrasound waves; whereas, an accumulation of a harder material, such as plaque, on the tissues may provide stronger reflections of different harmonics of the ultrasound waves. Based upon the relative strengths of the reflected fundamental and second harmonics of the ultrasound waves, a physician may be able to determine the presence and type of material within an area of interest.
It may also be appreciated that a larger area of interest may be treated or, if the area of interest is undesirable, disintegrated with the catheter of the second embodiment because the first ultrasound transducer and the second ultrasound transducer both may be directed at the area of interest. Further, since the difference ultrasound waves of the third embodiment may have fundamental harmonic substantially equal to the difference between the fundamental harmonic of the ultrasound waves created by the first ultrasound transducer and the fundamental harmonic of the ultrasound waves produced by the second ultrasound transducer, the difference ultrasound waves may be lower in frequency than either the ultrasound waves of the first ultrasound transducer or the ultrasound waves of the second ultrasound transducer. While propagating through the patient""s body, the difference ultrasound waves may be less subject to attenuation and may, therefore, experience a greater depth of penetration. Finally, it also will be appreciated that, through the use of catheters in accordance with the present invention, substantial savings in diagnostic and treatment costs may be passed on to patients required to undergo ultrasound diagnostic and/or treatment procedures, or to their insurers.